Date of Award

4-21-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Systems Engineering

First Advisor

Seshadri Mohan

Abstract

The increasing demand for bandwidth has played a critical role over the history of the development of wireless networks. For the 5G and beyond wireless networks, it is required to use communications systems able to support the massive connectivity and higher spectral efficiency that have good bit error performance as a measurement tool of the system reliability. Therefore, the cyclotomic construction method of a lattice is proposed for the SCMA-NOMA technique, and Ramanujan graphs are proposed for LDPC codes and the LDS-NOMA technique. The Cyclotomic construction ensures that the diversity of the mother constellation of SCMA is improved, which is the main reason the BER performance is enhanced compared to known systems of SCMA. On the other hand, an algebraic algorithm is proposed to construct highly symmetric Ramanujan graphs able to generate LDPC codes with minimized error floor. Therefore, they have better BER performance than the same LDPC codes family, and QC LDPC codes have similar codewords length. Furthermore, the algorithm is employed to construct the indicator matrix of the LDS-NOMA system. The BER performance shows an improvement compared to the performance of the same system with a different overloading matrix with a similar overloading ratio. Finally, the BER performance of the LDS-NOMA system based on the proposed graph has been compared to the same system with different overloading ratio scenarios, and the spectral efficiency was measured to show the effectiveness of using LDS-NOMA and SCMA in supporting the massive connectivity. The proposed SCMA, LDPC codes, and LDS-NOMA can be employed to meet the requirement of future wireless networks.

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